Windows Vista (with Aero running) only: Wheelie, a free beta app, can be used solely as a pretty neat application switcher at this point, but its developers seem to have much grander plans for the little utility. Once installed, you can flip through active window thumbnails with your mouse wheel by touching the top edge of the screen. Park the cursor there, however, type in a word or phrase, and your screen fills with results from (apparently) Google Image Search. It's important to note that Wheelie takes up a serious chunk of memory in its current beta state, but it's an intriguing experiment that at least offers an alternative to Alt-and-Tab-ing at this point. Wheelie is a free download for Windows Vista systems running Aero only.